The present invention relates generally to thermometers and more particularly to a thermometer that is capable of meeting the criteria of a truly disposable system which can replace the existing mercury in glass thermometers. The invention is particularly characterized by use of readily available materials, economy, ease of manufacture, lack of need to be activated prior to use, lack of special handling or storage requirements, easily discernible temperature responsive change and, further, providing patient comfort in that the measurement locus is one half as long as in existing systems and in that the insertion time is less than thirty seconds, consistent with covering the accepted range and accuracy for fever thermometers.
The principle utilized in many prior art disposable thermometers if the detection of a change in state of a temperature indicating substance. Systems differ in the choice of substances and in the detection means. The temperature indicating substances of prior art disclosures include adjacent members of the even number series of fatty acids, halogenated carbon waxes or a wide variety of white crystalline solids, all with melting ranges between 36.degree. and 42.degree. C. The detection systems utilizing such materials include movement of a liquid melt to a corresponding cavity, the use of indicators below solid substances which become visible because the compounds are transparent when liquid, and the absorption of a liquid melt into an indicating compound forming a eutectic mixture with the indicator system thereby generating additional liquid which facilitates visual detection. These disposable thermometers have deficiencies which result in devices that do not meet the necessary criteria for a disposable system. Prominent among these are the difficulty of distinguishing the precise temperature level reached; intended use of many such devices only as screening devices with five or less indicators; complicated construction, in some instances, involving up to seven layers of materials and intermovements in the system making them very costly to manufacture; and requirements of special handling during shipment and storage for irreversible versions or activation means for reversible versions in some devices. The advantages of such prior art products over the conventional mercury thermometer are offset by such limiting defects. p It is an important object of the invention to provide a disposable thermometer avoiding the above defects.
It is a further object of the invention to provide precise temperature indications consistent with the preceding object.
It is a further object of the invention to provide highly discernible temperature indications consistent with one or both of the preceding objects.
It is a further object of the invention to provide a reliably reversible thermometer consistent with one or more of the preceding objects.
It is a further object of the invention to provide a modular thermometer product line which can be rendered in reversible or non-reversible forms consistent with one or more of the preceding objects.
It is a further object of the invention to provide a small measurement locus consistent with one or more of the preceding objects.
It is a further object of the invention to provide low measurement time consistent with one or more of the preceding objects.
It is a further object of the invention to provide a low cost thermometer consistent with one or more of the preceding objects.